[Bug]: 500 when requesting `/api/files/upload_archive` concurrently

[un-def]

Steps to reproduce

# .dstack.yml
type: task
files:
  - blob
commands:
  - sleep 10

dd if=/dev/urandom of=blob bs=1M count=1

for i in {1..4}; do dstack apply --name task-$i --yes --detach & done

Actual behaviour

Only one run submitted:

dstack ps --last 4
 NAME             BACKEND       GPU  PRICE  STATUS      SUBMITTED
 task-4           ssh (remote)  -    $0     exited (0)  3 mins ago
 dev-environment  ssh (remote)  -    $0     stopped     1 hour ago
 dev-environment  ssh (remote)  -    $0     stopped     2 days ago
 dev-environment  ssh (remote)  -    $0     stopped     4 days ago

All other submissions failed with 500

Expected behaviour

No response

dstack version

0.20.15

Server logs

ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/home/def/dev/dstack/.venv/lib/python3.13/site-packages/sqlalchemy/dialects/postgresql/asyncpg.py", line 545, in _prepare_and_execute
    self._rows = deque(await prepared_stmt.fetch(*parameters))
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/def/dev/dstack/.venv/lib/python3.13/site-packages/asyncpg/prepared_stmt.py", line 176, in fetch
    data = await self.__bind_execute(args, 0, timeout)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/def/dev/dstack/.venv/lib/python3.13/site-packages/asyncpg/prepared_stmt.py", line 267, in __bind_execute
    data, status, _ = await self.__do_execute(
                      ^^^^^^^^^^^^^^^^^^^^^^^^
        lambda protocol: protocol.bind_execute(
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            self._state, args, '', limit, True, timeout))
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/def/dev/dstack/.venv/lib/python3.13/site-packages/asyncpg/prepared_stmt.py", line 256, in __do_execute
    return await executor(protocol)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "asyncpg/protocol/protocol.pyx", line 206, in bind_execute
asyncpg.exceptions.UniqueViolationError: duplicate key value violates unique constraint "uq_file_archives_user_id_blob_hash"
DETAIL:  Key (user_id, blob_hash)=(efa6c378-e86e-4738-b76a-57d1c9999e4b, c0265b5a6111efd917048b1cc50a3c6d0e23ff54756df49217d839915f0175a8) already exists.

Additional information

No response